1. Field of the Invention
The present invention generally relates to an engine with a valve lifter provided between an intake or exhaust valve and a camshaft.
2. Description of the Related Art
Conventionally, as a valve actuating mechanism of a DOHC engine, there is a so-called direct-acting type with a valve lifter (i.e., tappet) installed between an intake or exhaust valve and a camshaft. The valve lifter is formed in a shape of a cylinder having a base. The generally cylindrical valve lifter is slidably positioned within a guide opening formed in a cylinder head. The guide opening is formed on an axis that is generally coaxial with a stem of the associated intake or exhaust valve. The valve lifter is installed in the guide opening with the base (i.e., the substantially closed end) facing a camshaft.
The camshaft (e.g., an intake camshaft or an exhaust camshaft) in the valve mechanism of this type comprises multiple cams such that an associated cam presses the valve lifter. The cam shaft also comprises multiple journal surfaces that are rotatably supported relative to the cylinder head with associated bearings. The journal surfaces can be disposed at both ends of the camshaft and can also be positioned adjacent to the cams.
The bearing that supports each journal surface can be formed integrally with the cylinder head and can comprise a bearing main body that supports the journal surface from below while a cam cap can be secured to the bearing main body for supporting the journal surface from above.
In the conventional engine equipped with the valve mechanism described above, oil is supplied to the journal surfaces through an oil passage formed in the camshaft. The oil passage comprises an axial passage formed in the camshaft that is joined to radial passages positioned proximate the journal surfaces. The radial passages typically open through the cam shaft toward the bearing. An oil pump supplies oil to the axial passage.
Oil leaking from the journal region lubricates the space between the valve lifter and the guide opening. Such a construction is disclosed in JP-A-Hei 9-79019. In some configurations, a bowl-shaped oil holder generally surrounds the upper circumference of the guide opening of the valve lifter in order to use the oil leaking from the bearing to lubricate the valve lifter, as shown in JP-Y-2531392.